Sanitary napkins, also referred to as catamenial or feminine pads, are designed to be worn by a female to absorb medium to heavy flow of body fluids such as menses, blood, urine, and other excrements discharged by the body during a menstrual period. Sanitary napkins are external devices which are designed to be aligned approximate the pudendum region of the human body and are generally held in position by being adhesively or mechanically attached to an undergarment. Such products differ from tampons which are classified as internal devices and are designed to be physically inserted into the vaginal cavity. Sanitary napkins also differ from pantiliners and panty shields in several noticeable ways. Sanitary napkins are generally larger in size, have a more defined three-dimensional configuration, are thicker in caliper and are bulkier in appearance than pantiliners or panty shields. Functionally, sanitary napkins are different in that they are constructed to absorb a greater quantity of body fluid and are designed so that they can be worn for a longer period of time; for example, overnight if needed.
Since sanitary napkins are normally used during the major discharge portion of a menstrual period, they are constructed to handle medium to heavy flows and commonly have a total absorbent capacity in the range of about 20 to 50 grams of fluid. Pantiliners and panty shields, on the other hand, are designed to absorb relatively small amounts of body fluids and are marketed to be used at the beginning and end of a menstrual period when flow is light or spotty. Commercially available pantiliners and panty shields are constructed to have a total absorbent capacity in the range of about 1 to 15 grams of fluid.
Today's sociological changes have enabled women to become more active in sports and other types of physical activity. These changes have been complemented by a change in attire and have given women the option of wearing tight, body-fitting clothing. Current sanitary napkins, having a caliper of 6.4 mm or greater, can present an unsightly bulge adjacent the pudendum when worn inside tight-fitting shorts or pants. The overall size and configuration of the napkin can also restrict leg movement or cause discomfort when a women participates in physical or sporting events. In view of this, there is a real need to develop a thin sanitary napkin which is less than about 5 millimeters in caliper yet able to absorb as much body fluid as current available products.
In developing a thin sanitary napkin less than about 5 millimeters in caliper, it was realized that such products had a tendency to twist and bunch when worn. The squeezing of the napkin between the thighs and the resulting deformation as a woman moves about, causes the upper surface of the napkin to acquire a curved or convex shape. This twisting and bunching is referred to as "roping" because a cylindrical profile can be imparted to the sanitary napkin. This roping effect is detrimental because the napkin is unable to absorb body fluid that contacts its upper surface. The fluid discharged from the vagina has a tendency to run off the roped napkin before it can be absorbed and, therefore, the fluid leaks onto the undergarment. This run-off becomes significant during periods of heavy flow.
It has been found that by positioning an absorbent strip, which is stiffer and more absorbent than adjacent portions, along the longitudinal central axis of the sanitary napkin, this roping phenomenon can be mitigated and/or eliminated.
Other manufacturers have recognized the need for a thin sanitary napkin but have not addressed the roping problem. U.S. Pat. No. 4,950,264, issued to Thomas W. Osborn, Ill., teaches a thin sanitary napkin. The Osborn application teaches a thin sanitary napkin comprised of an absorbent and a liquid-impermeable barrier. Claim 1 teaches that the sanitary napkin has a flexure-resistance of less than about 300 grams, a test capacity of at least about 8.0 grams, and a total capacity of at least about 20.0 grams. The Osborn application also teaches that the thin sanitary napkin is under 5.0 millimeters in caliper and has a capacity sufficient to absorb medium or heavy flows. However, Osborn does not teach the presence of a longitudinally-extending central absorbent zone, which is less than about 2 inches wide, and which is stiffer and more absorbent than adjacent portions of the napkin.
U.S. Pat. No. 4,079,739 issued to Howard A. Whitehead and assigned to the present assignee teaches a feminine pad having a thick central layer of absorbent material. The thick central layer does not contain superabsorbent as does the laminate taught in the present invention.
Other patents, which teach various aspects of this invention, include the following: U.S. Pat. No. 3,065,751 issued to Gobbo et al. which teaches a disposable diaper having a certain Gurley stiffness and having a flexible absorbent layer; U.S. Pat. No. Re. 32,649 issued to Brandt et al. which teaches hydrogel forming polymer compositions for use in absorbent structures and at column 18, lines 40-43, mentions the thickness of the absorbent core; and U.S. Pat. No. 4,578,068 issued to Kramer et al. which teaches an absorbent laminate structure containing superabsorbent particles.
Now, a thin sanitary napkin has been developed which has a longitudinally-extending central absorbent zone which is less than about 2 inches wide and which is stiffer and more absorbent than adjacent portions of the napkin.